This invention relates to improvements in solenoid-controlled valve assemblies especially but not exclusively for vehicle hydraulic braking systems, for example for braking systems of the electro-hydraulic type.
Known solenoid-control valve assemblies for use in electro-hydraulic braking systems typically comprise a spool working in a bore in a body or sleeve in which movement of the spool acts to connect and disconnect passages for providing fluid communication between an hydraulic power source, a brake and a reservoir. The valve usually further comprises a solenoid comprising a coil and an armature whereby energisation of the coil produces a force which displaces the armature, in turn to apply a force to the spool, to bias the spool towards one end of the bore. The force applied by the armature is resisted by a biasing means, typically a coil spring, which acts upon the spool to oppose the biasing force applied by the armature. In a most typical arrangement, the armature acts directly upon one end of the spool whilst the biasing spring acts upon the other end of the spool.
In accordance with a first aspect of our invention, in a solenoid-controlled valve assembly comprising a spool working in a bore in a body, at least a first flow passage and a second flow passage defined in the body each connecting at one end with the bore, movement of the spool within the bore being adapted to connect and disconnect said first and second flow passages, a solenoid comprising a coil fixed relative to the valve body and an armature, application of a current to the coil causes the armature to apply a force in a first direction to the spool, and a biasing means adapted to apply a resisting force to the spool in a second direction opposite to the direction substantially of the force applied by the armature, and in which engagement between at least one of the spool and the biasing means and the spool and the armature is through an engagement means defining a single point of contact.
Thus, according to the invention, the area of contact between the spool and the biasing means and/or armature comprises a single point contact. This point contact is preferably on the axis of the spool.
By providing a point contact between the spool and the biasing means, side forces acting upon the spool (ie. orthogonal to the spool axis) and friction are reduced and so the spool diameter can be reduced without risk of jamming. Also, tolerances between spool and the bore can be tightened.
The engagement means may comprise an integral part of the spool, biasing means or armature.
Preferably, the engagement means comprises a ball like member which is adapted to provide the engagement between the spool and the biasing means. The ball may be adapted to sit within a recess provided in the end of the spool on the axis of the spool.
The biasing means may comprise a resilient and an engagement member which is positioned between the spring and the spool. The engagement member may comprise a cup 56, as schematically illustrated in FIG. 3, which sits in the end of the spring and provides a surface (facing away from the spring) which engages the ball at a center position. The engagement member is adapted to be displaced out of its plane of rest when a force is applied to the ball along the axis of the spool, in turn to compress the spring.
The armature may be adapted to act upon an intermediate member which is adapted to act upon an end face of the spool whilst the opposite end face of the spool acts upon the biasing means through a single point engagement.
The intermediate member may comprise an elongate guide rod adapted to fit loosely within a guide bore defined in a guide body. The guide body may be fixed relative to the valve body which defines the bore in which the spool operates. The guide is preferably axially aligned with the bore in which the spool operates.
By providing the intermediate member between the armature and the spool, it is possible to substantially reduce any risk of side forces being applied to the spool when the armature is displaced by the magnetic forces generated in the coil. The gap between the intermediate member and the walls of the bore prevents friction between the two, although the bore helps in aligning the intermediate member during assembly.
The engagement between the intermediate member, the armature and/or the spool may be through a respective single point of contact.
Of course, it will be understood that the engagement between the spool and the biasing means may be direct contact between the two or indirect contact through an engagement member, such as cup shaped member and the ball already proposed herein before. For example, the end of the spool may be domed or sharpened to a point and engage directly with the biasing means.
In a most preferred arrangement, the biasing means may comprise a coil spring arranged concentrically with a line passing through the axis of the spool, which may act upon the spool through an intermediate member such as a cup or an annular disc, the engagement between the centre of the disc and spool defining a point contact. This arrangement results in a reduction in side forces in the spool.
The spool may work in a bore defined in a sleeve in a body. The spring may then be fixed relative to the sleeve.
In accordance with a second aspect of our invention (as schematically illustrated in FIG. 2) in an electro-hydraulic braking system comprising a source of pressurized fluid 40, a reservoir 34, at least one brake actuator 38, and a solenoid-controlled valve assembly 32 according to the first aspect of the invention, the valve assembly includes at least three substantially radial flow passages, a first passage being connected to a pressure source, a second passage connected to the reservoir, and a third passage connected to the brake.
According to a yet further aspect of our invention, in a solenoid-control valve assembly, comprising a spool working in a bore in a housing, and at least a first and a second flow passage, each passage extending through a wall of the housing and having a first end opening into the bore and a second end communicating with the external surface of the housing, the spool is provided with at least one land adapted to connect and disconnect the two passages, and the first ends of the two passages are spaced apart in a direction parallel to the axis of the bore by a smaller distance than the spacing between the second ends of the passages.
The housing may comprise a unitary body, or sleeve housed in a bore in a body.
The invention thus enables a spool of relatively short axial length to be provided because of the close spacing between the first ends of the passages.
Preferably, at least one of the passages is inclined at a non-zero angle relative to the axis of the bore and to a plane orthogonal to the axis of the bore, ie. the passage extends radially but not orthogonal to the bore axis.
One or more of the other passages may extend radially orthogonal to the bore.
In a most preferred arrangement, three radial passages may be provided, one inclined at a non-zero angle relative to the axis of the bore and a plane orthogonal to the axis of the bore, one orthogonal to the bore and the other inclined at an opposite angle to the first passage. This balances out the axial components of forces due to fluid in the passages acting upon the spool. The two inclined passages may be provided on either side of the orthogonal passage.
The passages may thus form an arrow head shape comprising V-shape formed from the first and third passages which is dissected by the second passage, the head of the arrow being at the bore in the sleeve.
The two or more passages may extend radially from the bore in a single plane containing the axis of the bore.
In one arrangement, the passages are formed by drilling through the housing into the bore to form straight passages.
Each passage 50, 52, 54 may comprise part of a set of passages consisting of one or more corresponding passages inclined at the same angle which are spaced circumferentially around the bore. For instance, each passage may have a single corresponding passage provided on the diametrically opposed side of the body, as schematically illustrated in FIG. 3. Alternatively, three passages spaced at 120 degree intervals may be provided. This helps to balance any side force components acting on the spool due to the pressure of any fluid in the passages. Each passage and its corresponding passage or passages may be interconnected by an annular flow space defined around the outside of the body. When the bore is defined in a sleeve located in a larger bore in a body, the flow spaces for each set of passages may be isolated from adjacent flow spaces by one or more elastomeric seals connecting the body to a sleeve which surrounds the body. FIG. 4 is a schematic view of a cross section of the sleeve 3 illustrated in FIG. 3. FIG. 4 illustrates one set of passages 50 interconnected by a flow space to a source of pressurized fluid 40.
A number of ports may be provided in the housing around the sleeve to allow an external fluid line to be connected to each flow space. Where three passages are provided, one flow space may be connected to a reservoir, the other to a brake and the other to a source of pressure fluid. The valve may therefore comprise a part of an electro-hydraulic braking system with connections between the valve and the remaining portions of the system as described above. Of course, the valve could be connected to the brakes in any other manner, and may have two or more sets of passages.
A first passage may be connected to a fluid reservoir. A second passage may be connected to a brake. A third passage may be connected to a source of pressurised hydraulic fluid.
A filter may be provided at or across the end of each or some of the passages at their second end away from the bore. The filter may help to prevent debris and contaminants entering the bore containing the spool.
The diameter of one or more of the passages may be stepped or may be of a single constant diameter.
There will now be described, by way of example only, one embodiment of the present invention with reference to the accompanying drawings of which: